The present invention relates to data communications systems, and more particularly to data communications systems which utilise telecommunications apparatus arranged to operate in accordance with a telecommunications standard, wherein analogue signals are communicated in a digital form.
In order to create a telecommunications network from inter-connected items of telecommunications equipment, manufacturers arrange for such items of telecommunications equipment to operate in accordance with a telecommunications standard. Such telecommunications standards are agreed between manufacturers of telecommunications equipment so that equipment may be interchangeable with other manufacturer's equipment, thereby providing a means whereby telecommunications networks may be constructed from equipment supplied from different manufacturers.
It has become well established in the telecommunications art to communicate analogue signals via telecommunications systems, by representing the analogue signals in a digital form. By representing analogue signals in a digital form, a substantial immunity to the effects of noise inevitably introduced by the telecommunications system is provided.
Pulse Code Modulation (PCM) is an example of a known technique for communicating analogue signals in a digital form. Pulse Code Modulated signals are generated by sampling the analogue signals to be communicated, in accordance with a predetermined sampling rate, and digitally representing the amplitude of each sample. Successive temporally displaced signal samples representative of the analogue signals are thereafter transported via the telecommunications system to a receiver. The receiver operates to re-generate the analogue signals from the PCM samples. To further improve capacity of a telecommunications system, in terms of the number of analogue signals which may be communicated with a given bandwidth, a coding technique known as Adaptive Differential Pulse Code Modulation (ADPCM) may be used in order to reduce an amount of data required to represent PCM data samples. Adaptive Differential Pulse Code Modulation has for this reason become a standard media by which analogue signals or speech data are transmitted over telecommunications systems. As such ADPCM has become embodied in telecommunications standards to the effect that a substantial quantity of telecommunications equipment operates to transport speech data in a form of ADPCM.
The field of wireless data communications is no exception. For example the Digital Enhanced Cordless Telecommunications standard (DECT) is a cordless telephone standard developed by the European Telecommunications Standards Institute for short range wireless communications. A wireless telephone system arranged to operate in accordance with the DECT standard communicates analogue voice band signals in a form of ADPCM data.
In a situation where it is required to communicate digital data over a telecommunications system arranged to operate in accordance with a telecommunications standard, a requirement that information to be communicated must be presented to encoders of the system in an analogue form becomes a technical problem. This is because, for example, PCM and ADPCM encoders are arranged to convert analogue data signals into digital signal samples representing the analogue signal. Therefore in order to communicate digital data using such standard telecommunications equipment, the data must be converted into analogue signals before the data can be communicated using the equipment. This has an effect of substantially reducing a rate at which data may be communicated over such a system.